This invention relates to continuous multi-furnace heat treating systems and particularly to a furnace system wherein multiple rotary furnaces are employed to simultaneously process, in a single system, parts requiring different heat treatment cycles.
Existing continuous carburizing furnace systems frequently include different sections or chambers for separating the various treatments employed in the carburizing processes--namely, heating, carburizing, diffusion, and equalize cooling. For example, U.S. Pat. Nos. 3,598,381 and 3,662,996 describe apparatus having separate furnace stages, generally rectangular in plan view, for heating, carburization, and diffusion of metal parts at selected temperatures and in different gaseous atmospheres for specified periods of time. In such systems trays of parts are pushed or pulled one after another through each furnace in a fixed sequence, with each tray remaining in the same relative position in its line throughout its passage through the system. Each part receives an identical heat treatment.
Although the above-mentioned systems have been widely used for continuous, lengthy runs of similar parts, they are not well-suited for plants in which it is necessary to process a variety of metal parts which require different cycle times and/or different types of quenching/cooling, and where it is desired to "manufacture-on-demand" a variety of parts so as to maintain low inventories. For example, the systems of U.S. Pat. Nos. 3,598,381 and 3,662,996 would be cumbersome to utilize for such applications because they generally can achieve different heat treatments only by partial or complete unloading of a line through the use of empty trays in selected portions of a processing line. Such approaches are time-consuming and substantially reduce efficiency of a furnace system.
Limited attempts have been made to provide greater flexibility of processing parts in furnace systems by the use of a single rotary hearth carburizing furnace, as disclosed at pages 19 and 21 of Metal Progress (September 1985). Also, FIG. 6 of U.S. Pat. No. 3,598,381 shows a rotary hearth diffuser providing a diffusion chamber separate from a conventional carburizing chamber. While these systems offer some improvement, they allow part processing times to be varied only in a single portion of the total heat-treating process. Moreover, the rotary hearth furnaces disclosed in these prior art systems do not permit adequate zoning of their rotary furnace chambers into multiple zones or chambers for improved temperature control. Also, such single chamber rotary furnaces would require hot pulling mechanisms for the transfer of trays of parts between two rotary furnaces, decreasing the reliability of transfer and reducing accessability of the transfer mechanisms for maintenance.
Accordingly, it is an object of the invention to provide an improved furnace system wherein various parts are heat-treated for different periods of time while being processed through the system in adjacent trays and without requiring the use of specified numbers of empty trays in the system.
It is an object of the invention to provide a furnace system which simultaneously runs parts having variable heat-treating cycle times while maintaining the highest level of efficiency.
It is an object of the invention to provide a furnace system with multiple, interconnected chambers several of which simultaneously heat treat parts with different processing time requirements.
It is an object of the invention to provide a furnace system which, in addition to the above, moves parts between chambers solely by pushing action and without intermixing of the atmospheres of interconnected chambers.
It is an object of the invention to provide a multi-chamber furnace system wherein in each of several chambers a tray of parts, regardless of its position, may be selected as the next tray to be discharged from that chamber.
It is an object of the invention to provide a furnace system with a rotary-hearth carburizing furnace having multiple temperature-controlled zone and improved circulation of its gaseous atmosphere.
It is an object of the invention to provide a furnace system with multiple rotary chambers having improved uniformity of temperature and atmosphere within each chamber.
It is an object of the invention to provide a multi-chamber furnace system wherein any tray of parts within a rotary equalizing chamber may, regardless of position within the chamber, be directed to a selected discharge door for quenching/cooling in one of multiple apparatuses of different types.
It is an object of the invention to provide a furnace system with multiple rotary furnaces including an equalizing furnace which is operable to cool parts, to transport parts to a slow cool apparatus and/or to selected quench devices, and to reheat parts returned from the slow cool apparatus.